1. Field of the Invention
This invention relates to network communications and more particularly to redundancy of routing protocols, such as the Open Shortest Path First (“OSPF”) protocol and apparatus for protecting protocol services of a router and neighbor routers from failure.
2. Related Art
The Internet Protocol (“IP”) is the foundation for many public, such as the Internet, and private, such as a corporate Intranet, data networks. Convergence of voice, data and multimedia networks has also been largely based on IP-based protocols.
Data packets progress through the data networks by being sent from one machine to another towards their destination. Routers or other types of switches are used to route the data packets over one or more links between a data source, such as a customer's computer connected to the data network, and a destination. Routing protocols such as Border Gateway Protocols (“BGP”), Routing Information Protocol (“RIP”), and Open Shortest Path First Protocol (“OSPF”) enable each machine to understand which other machine is the “next hop” that a packet should take towards its destination. Routers use the routing protocols to construct routing tables. Thereafter, when a router receives a data packet and has to make a forwarding decision, the router “looks up” in the routing table the next hop machine. Conventionally, the routers look up the routing table using the destination IP address in the data packet as an index.
In the basic OSPF algorithm, a router broadcasts a hello packet including the router's own ID, neighbors' IDs the router knows and also receives such messages from other routers. If a router receives a Hello packet, which includes its own ID, from another router that the router has been aware of, on the understanding that the two routers have become aware of each other, the two routers exchange network link-state information by sending routing protocol packets. The router creates a routing table based on the network link-state information collected by running the link-state routing algorithm, typically the Dijkstra algorithm. In OSPF, the routing table can specify the least-cost path, based on a cost determined by considering many factors including network link bandwidth, as the packet route. When a network link changes, each router calculates the shortest path for itself to each of the networks and sets its own routing table accordingly to the paths. A route calculation unit is used for creating a routing table.
Each router, while it transmits or receives control packets and network link-state information, manages the states of other routers on the network to which this router is connected and also manages the states of the interfaces through which this router is connected to networks. With regard to the states of routers, each router manages the routers' ID's, and checks if each of those routers is aware of this router, or checks if each of those routers has completed the transmission and reception of network link-state information. With regard to interface state, each router manages the addresses of the interfaces and other routers connected to a network to which an interface is connected.
When conventional IP edge routers lose their primary circuitry and operation falls back to a redundant controller, a five to fifteen minute outage ensues while the router releases the routing states and packet forwarding tables. In order to enhance the reliability of the router device, it is important to multiplex the above-mentioned route calculation units. The multiplex router device includes a plurality of route calculation units, and always has one route calculation unit placed in the active mode to make it execute an ordinary process while keeping the remaining route calculation units in a standby mode. When the route calculation unit in the active mode runs into trouble, the multiplex router device brings one of the waiting route calculation units into the active mode (this is referred to as a system switchover of route calculation units), and the one other route calculation unit takes over and continues to execute the process that was previously being executed by the route calculation unit in trouble.
U.S. Pat. No. 6,049,524 describes a multiplex router device which reduces the amount of information to be transmitted from a route calculation unit in operation to a route calculation unit in standby mode. The route calculation unit in the active mode is connected by an internal bus to the route calculation unit in the standby mode. The route calculation unit in the active mode stores network link state information showing connections of the router and other routers with networks, neighboring router states showing states of neighboring routers and interface states showing states of network interfaces to connect the multiplex router device to the network. The route calculation unit in the active mode sends to the route calculation unit in the standby mode only the network link state information. In the route calculation unit in the standby mode, a database integration module that received the link-state information stores its contents in a link-state database. When a failure occurs in the route calculation unit in the active mode, the route calculation unit performs the routing protocol process by using the stored link-state database, so it is not necessary to exchange information with other routers to collect the network link state information over again. For awhile after the switchover to active mode the route calculation unit has no information about the neighbor route state and interface state. Hello packets are transmitted from the route calculation unit brought into the active state. The route calculation brought into the active state gradually accumulates information about the neighbor router states and interface states in order to gradually bring a complete list of ID's of other routers which is included in later Hello packets that the route calculation unit sends out.
It is desirable to provide high network availability by providing improved redundancy which can be implemented as a link level protocol running over IP having a backup link level process in total real time synchronization with an active one in order to enable an expeditious switchover when a failure occurs on the active control card.